Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: December 15, 2000
Publication Date: N/A
Interpretive Summary: Drainage restrictions have caused salinity problems in irrigated agriculture on the west side of the San Joaquin Valley of California. The restrictions were put in place when accumulations of selenium reached toxic levels in the reservoir receiving these waters. Subsequent studies have identified phytoremediation as one approach to reducing levels of selenium in drainage water and soils. Phytoremediation refers to the use of plants that accumulate the element in question in their tissues. When harvested, disposal or reuse of the crop biomass essentially removes the element from the production cycle. Plants used for phytoremediation of selenium have been shown to be sensitive to boron in soil or irrigation water. Recent research describes a few plants as being phytoremediation alternatives for boron reduction, but with limited success. If boron can be reduced in drainage water, phytoremediation techniques would be more widely applicable. An ion exchange column was tested using a boron-selective resin. Drainage water was processed for boron reduction. The ion exchange resin selectively removed boron from the flow. When the resin was fully loaded with boron, a regeneration cycle removed boron from the resin. The resultant regenerant was a dilute sulfuric acid solution with boron. Such a solution could be injected in drip irrigation as a fertilizer and cleansing agent in boron deficient areas.
Technical Abstract: This project investigated the behavior of a boron-specific ion exchange resin for processing water sampled from an agricultural drain. The process water was stored in a tank that served as the supply reservoir for the ion exchange column. A peristaltic pump supplied the column with water for treatment and samples of effluent were automatically collected with a sequential sampler. Samples were analyzed for boron. Results indicate th resin is capable of boron removal to levels undetectable with mg/L precision during the first 17 hours of column operation. The boron level in the process water was 8 mg/L with several other contaminants present. A treatment capacity on the order of 200 resin bed volumes was achieved. A regeneration cycle removed boron from the resin in preparation for the next cycle of drainage water. The regenerant was analyzed for boron to characterize the regenerant cycle. Boron was removed from the resin in the efirst half of the four-hour regenerant cycle. Analyses of samples from th last two hours of the regenerant cycle indicated that boron was at or below the detectable limits of the laboratory procedure. The regenerant can be used as a micronutrient fertilizer and cleaning agent for injection in drip irrigation systems. Using good quality water in preparing the acid regenerant solution would minimize processing costs for the fertilizer. Analysis of used regenerant indicated that only boron and sulfuric acid were in the solution. The initial cost and treatment data suggest a potential for mitigation of boron in agricultural drainage water.